The present invention relates to a new and improved method of embossing metal parts, and particularly to an embossing method using a non-collapsible mandrel.
Generally, an internally-embossed tubular or cup-shaped part is made by extruding a blank with a pre-embossed surface through a die onto a smooth mandrel. This method causes distortion of the embossed portion during the forming operation.
In accordance with the present invention, the desired embossed part is made by extruding a smooth-surfaced preformed blank through a die onto a non-collapsible mandrel having an external surface counter to the desired internal embossment, and hydrostatically expanding the embossed blank, or an embossed portion thereof, from the mandrel, permitting removal of the part and forming an undistorted embossed pattern on the internal surface, or portion thereof, of certain tubular or cup-shaped parts. The step of extruding the blank through the die onto the patterned mandrel may include the application of hydrostatic pressure to the exterior of the blank.